a. The regular expression (b + ab) *(a + ab) * describes the set of all strings in {a, b}* not containing the substring. for any x. (Fill in the blanks appropriately.) b. The regular expression (a + b) *(aa*bb*aa* + bb*aa*bb) (a + b)* describes the set of all strings in {a, b}* containing both the substrings and (Fill in the blanks appropriately.)